What does random assignment accomplish in an experiment?

What does random assignment accomplish in an experiment?

• A. Random assignment allocates participants to groups by chance, helping equalize groups and reduce bias.
• B. Random assignment guarantees no confounds exist.
• C. Random assignment ensures the same participant is in every condition.
• D. Random assignment is used only in surveys.

Answer: (A)

Random assignment places participants into groups by chance, so the groups are likely to be similar on both measured and unmeasured characteristics. This helps ensure that any differences observed after the treatment are due to the treatment itself rather than preexisting differences, reducing bias and potential confounding variables. It does not guarantee that all confounds are eliminated—randomness can still leave some imbalances by chance or through issues like small sample sizes—but it greatly increases the likelihood that group differences reflect the manipulated variable. It also isn’t about having the same participant in every condition—that describes a within-subjects design. And random assignment is a hallmark of experiments, not something used only in surveys.

Random assignment places participants into groups by chance, so the groups are likely to be similar on both measured and unmeasured characteristics. This helps ensure that any differences observed after the treatment are due to the treatment itself rather than preexisting differences, reducing bias and potential confounding variables. It does not guarantee that all confounds are eliminated—randomness can still leave some imbalances by chance or through issues like small sample sizes—but it greatly increases the likelihood that group differences reflect the manipulated variable. It also isn’t about having the same participant in every condition—that describes a within-subjects design. And random assignment is a hallmark of experiments, not something used only in surveys.